APEM Zeroes In On Birds in Flight

Scientists at APEM have developed a new technique for measuring the height of birds in flight expected to ease concerns about the potential dangers of wind turbines for birds and lead to improved outcomes for developers of offshore wind farms.

The results are based on analysis of an aerial survey carried out last November. One of APEM’s specialist survey aircraft was fitted with ultra-high resolution Leica RCD-30 survey camera, matched with a LiDAR system.

During the survey, the aircraft flew at an altitude of 340m and gathered images and LiDAR data of a swath of land 346m wide. As it flew, the system recorded information on features of the landscape as well as on birds in flight, both in flocks or as individuals.

Once the data were processed into digital images, researchers were able to pinpoint the heights of birds on the wing to within 5cm, a level of precision far greater than needed for the assessment of collision risk around wind farms, APEM said.

Although the survey took place over land, exactly the same technique can also be used to measure the flight heights of birds at sea, according to APEM.

APEM’s head of ornithology, Dr Mark Rehfisch, said: “A LiDAR-based approach is the future of flight height assessment in open terrain. It is very precise and accurate, it generates a permanent record, it can be applied rapidly over large areas of open habitat, and it will become increasingly affordable as the technology is taken up.”

Previous methods for measuring the flight heights of offshore birds have relied upon visual estimates from observers in boats, measurement using laser rangefinders by people stationed on offshore wind turbines, or on data from GPS tags attached to the birds.

Sophie Nunn, APEM’s project manager in charge of testing the new technique, said: “We had already developed a way to successfully estimate flight heights from high resolution aerial images, but this approach requires the birds to be flying straight and level and this is not always the case. Our new technique is a major step forwards because it provides very precise data, regardless of the orientation of the bird.”